What I haven't figured out is, how do you pass function pointers
in the driver out to an application?
Mac OS 9 drivers are CFM Fragments. Apps use USBGetNextDeviceByClass
(USB.h) to find the proper device and get USBDeviceRef and your code
fragment connection id. They then use FindSymbol API
(CodeFragments.h) to get TheUSBDriverDescription (you're required to
export this symbol) and TheUSBClassDriverPluginDispatchTable (you're
required to export this as well).
You can, however, export other symbols, but it's annoying to call
FindSymbol 10 times and make function pointer for everything. The
better approach would be to make your own version of the
DispatchTable which is "longer" than the required one and has more
callbacks or do everything through device control function (from the
look of the app). In the former case you export some kind of global
variable (a structure pointer). Application gets this structure
pointer (dispatch_table) and then uses
dispatch_table->functionpointer(parameters); That's they way it calls
into your driver.
I'd like to have a function like
Move(pan,tilt) in the driver, that I can call from an application, once
the driver has done the initialization work. As was mentioned, the DDK
documentation was written for someone who knows what he's doing,
that's not me, yet.
I've had the same felling about the docs.
The example I've most studied, the USBKeypad
example, hangs around in an interrupt loop, talking to internal ADB
structures, and doesn't talk to outside applications. Do I have to call
USBGetNextDeviceByClass() etc. from the application?
Sure. That's how app finds your device. The better would be to look
at HIDReader. You'll find out how it works.
-Tomas
--
Ing. Tomas Zahradnicky, Jr.
Production Manager, 24U Software
Associate Member, Filemaker Solutions Alliance
mailto:email@hiddenhttp://www.24uSoftware.com
_______________________________________________
usb mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/usb
Do not post admin requests to the list. They will be ignored.
